A conventional force sensing apparatus includes a strain producing body which is elastically deformed when an external force is applied thereto and a plurality of sensing elements formed on the body and having an electric resistance changing in accordance with a deformation of the body. This apparatus takes out a change of the electric resistance as an electric signal of those sensing elements to sense the applied external force.
Generally, in a force sensing apparatus of this type, an external force acts on a point of action and can be decomposed into a number of components in accordance with the direction in which the external force acts.
There are several force sensing apparatuses which include a strain producing body of a cubic block structure which separately senses respective components of an external force applied thereto. These are disclosed in Laid-Open Utility Model Application Nos. 11903/1979 and 21021/1979, Laid-Open Patent Application Nos. 95433/1984, 57825/1986, 79129/1986, etc. Especially, these applications are characterized in that the force components Fx, Fy and Fz in the directions of X, Y and Z axes and the moment components Mx, My and Mz around the X, Y and Z axes of the external force are separately sensed by strain gauges attached on several surfaces to which the directions of the corresponding force components are perpendicular respectively. Thus the strain producing body cannot avoid taking the form of a three-dimensional structure as a block structure, as described above.
So long as such structure is concerned, means for manufacturing the strain producing body is limited to metal machining and/or electric discharge machining techniques. This means that it is necessary to manufacture the body from a block-like workpiece, which is difficult and troublesome. Further, such strain gauges attached so as to sense the corresponding force components must to be electrically connected in a bridge circuit, which means that the wiring is troublesome. Thus it is difficult to make them compact and reduce the manufacturing cost, and productivity is low accordingly.
Another example is a cubic block of combined plates, etc., to separately sense the respective external force components, as disclosed in Laid-Open Patent Application No. 83929/1986. A problem in this structure is that reproductivity is low because the sensing surfaces for the respective force components are fastened by screws, etc., which is likely to cause a hysteresis or non-linearity due to a deformation of the fastened surface portions.